Two antenna connectors are generally employed in mobile radiotelephones. One is connected to the antenna for use when the telephone operates as a portable device and the other is used when the radiotelephone is mounted in a car. The car antenna is switched into operation through the auxiliary antenna connector with the aid of an antenna change-over switch of the radiotelephone.
At present the most broadly employed connector types rely on a galvanic contact, whereby they exhibit the following disadvantages:
the connecter surfaces become worn and corroded over time;
the connectors are easily damaged by mechanical stresses;
the connectors are visible, and they can only be concealed in the telephone body using a separate protecting lid or the like.
Depending on the connector type there may exist further disadvantages:
the connector must be exactly aligned when mounted into the rack in a car (e.g. a common coaxial connector);
the connector occupies a large space inside the telephone (this is the case with most present connectors);
the connector easily becomes dirty (e.g. a coaxial connector);
the connector is expensive (e.g. specially made surface mount connectors).
Recently it was realized that it is advantageous to employ a capacitive RF connector which comprises two pairs of metal plates. A pair of smaller metal plates constitutes the inner conductor of the RF interface for the coaxial cable and a pair of larger plates constitutes the outer conductor of the interface. This outer conductor is formed by the metallic body of the telephone and has a size, e.g., of 6.times.18 cm, and constitutes the sheath of the coaxial cable.
Because the earth (ground) conductor is disconnected with a capacitor, the capacitance must be high in order to achieve a low attenuation. In a known implementation, this was solved by utilizing the metallic body of the telephone. On the other hand, the capacitances of the inner conductor capacitors must also be relatively high, because the signal transmission is carried out at a relatively low impedance level (about 50 ohms).